The invention relates to a rotor spinning machine and, more particularly, to a rotor spinning machine with a plurality of spinning stations, each of which comprises an opening roller and a draw-in roller for supplying a fiber band, such as a sliver, to the opening roller and control devices for individual drives of the draw-in rollers.
In the production of yam, a uniformity of the yarn which is as high as possible is generally aimed for within narrow tolerances. In contrast, the non-uniformity of the yarn is characteristic of effect or novelty yarns. A yarn, in which thick locations with predetermined larger diameters and with predetermined lengths, the so-called effects, are present, is called an effect or a novelty yarn. The yarn sections located in between with a smaller diameter are called webs. Effect or novelty yarns are becoming more and more important. Areas of application are, for example, denims, materials for casual clothing and home textiles.
Effect or novelty yarns can also be produced on rotor spinning machines. In order to produce effects in the yarn on rotor spinning machines, the sliver feed to the opening roller of the rotor spinning device is changed, for example, in that the speed of the take-in rollers is varied. Mechanical gearings, which drive shafts which extend along the length of the machine, are activated for this purpose. The draw-in rollers are made to rotate by means of these shafts. However, due to the large mass of the moved parts of a drive system of this type and the gearing play, a precise and abrupt change in the yarn thickness cannot be achieved, or only with difficulty, at the beginning and end of an effect. The speed during spinning of effect or novelty yarn optionally has to be sharply reduced compared to the speed when spinning effect-free yarn.
The basic German Patent Publication DE 44 04 503 A1 describes a rotor spinning machine, in which each draw-in roller with its drive shaft is directly connected to an associated stepping motor. Each stepping motor can be activated via an activation unit. Random speed changes of the sliver draw-in can be generated with a random generator. An effect or novelty yarn with predetermined effects cannot be produced with this known rotor spinning machine.
In order to set up a rotor spinning machine in such a way that it is possible to produce effect or novelty yarn with predetermined properties of the effects, a substantially outlay with corresponding costs for control devices and optionally also for the drives is necessary. For costs reasons, an outlay of this type is dispensed with in new rotor spinning machines, if the intention is not to spin effect or novelty yarn at the time of purchasing the machine. Thus, until now, only a small proportion of rotor spinning machines corresponding to the production proportion of effect or novelty yarn in the overall production of yarn has been equipped for the production of effect or novelty yarn. Since, in taking up the production of effect or novelty yarn, instead of new machines, it is often desired for economic reasons to use existing rotor spinning machines, which are however not accordingly equipped, and high costs are incurred for retrofitting. Control devices, which are adequate for controlling the production of effect-free yarn, are also not in a position to assist the production of effect or novelty yarn.